It is well known to measure electromyographic (EMG) signals from different parts of a human body during sports performances, the most common example being hear beat measurement using a surface EMG sensor-containing heart beat belt with a wireless transmitter module for communicating with a monitoring device, such as a sports watch. Measurement of surface EMG signals also from other parts of the body to monitor muscle activity in legs, arms, middle body or torso, for example. Such measurements can be carried using EMG sensors for example integrated into sports garment. It is also known to integrate signal transmitter modules into the belt or garment or to provide the module as a snap-on module to an assembly zone on the garment or belt. The module can be removed for washing the garment, for example. One disadvantage in known systems is that, although the transmitter can be removable and re-connectable, each sensor or sensor group requires a specifically designed transmitter module in order to operate properly.
To mention some specific examples, U.S. Pat. No. 8,253,586 discloses a performance measuring system comprising an article of clothing with an integrated measuring sensor and additionally a communication module, power module and computing module attachable to the article of clothing. The modules can be removed from one article of clothing and used in another article of clothing, while the sensor remains in the article. EP 1531726 discloses the use of a multitude of surface EMG electrodes to gain information simultaneously from muscles in various parts of the body. Also U.S. Pat. No. 4,583,547 relates to a similar application and in particular how conductive paths in garment can be arranged to provide a sensor signal form the measurement point to the signal transmitter module.
U.S. Pat. No. 7,698,101 discloses a system for pairing sensor-containing shoes with measurement electronics, including authentication of the shoes for the electronics. These solutions require dedicated transmitter module sensor pairs in order to be able to transmit the measurement signal to a monitoring unit.
Document WO-A-90/14792 discloses a biofeedback device for monitoring muscular activity in a sports skill movement which includes a band for securement around a muscle and carries a pair of spaced electrodes for receipt of electrical voltage from the muscle surface. The electrodes are connected to a differential amplifier and means for reporting the amplified voltage to indicate muscle tension over a continuum of the movement.
US 2013/0096704 discuss articles of clothing and module capable of sensing physical and/or physiological characteristics associated with the use of the clothing. The module contains an integral sensor. The system can activate module upon engaging the module to the clothing and confirm that the clothing and the module are authorized for use with one another and/or for automatic algorithm selection. The flexibility of the system is, however, restricted to adaptation of the sensor module to use its built-in sensor in different ways depending on the clothing it is attached to. Thus, a plurality of modules is needed if different types of sensors are used.
US 2008/0319330 disclose as a further example of currently available techniques a mobile transmitter for observing performance-related events and transmitting data on the observed events to a receiver. The transmitter comprises a timer for providing time references relating to the events and a memory for recording time references. The transmitter obtains a time reference from the timer and records the obtained time reference in the memory and is adapted to produce data messages containing a predetermined number of time references obtained from the memory and further to transmit the produced data messages to the receiver. The disclosed system allows for time stamping of events, such as heartbeats, and calculating the frequency and/or interval variation parameters of heartbeats. The system does not allow for synchronizing events from different detector sources.
One problem also touched by the above mentioned publications in a multi-sensor system is the communication of the different EMG measurement signals to a single monitoring device. There are systems, which utilize wired communication channels from a plurality of sensors to a single module. Such systems become impractical if there is a need to use many sensors at distant body parts and potentially separate belt or garment units.
Related prior art does not show any means how to minimize wiring in order between sensors and monitoring devices in applied health science. To provide a power signal to components like EMG sensors both power and EMG signal wires are used. Wireless approaches are envisaged e.g. in the aforementioned U.S. Pat. No. 7,698,101. However, to make each sensor an complex circuit with an integrated active RFID component, would be impractical both in medical applications where electrodes are usually disposable and wireless connections are often not allowed, and in sporting goods where electrodes need to be very thin, light and thoroughly washable.
A further aspect of the same problem in existing systems is how to handle signals from a plurality of sensor sources such that an overall analysis of the performance would be possible. The more sensors, the more wiring is needed in the garment or clothing. As such, a monitoring unit can relatively easily collect data from several sources, but may still lack information on the relationship between the data and the performance.
Thus, there exists a need for improved solutions for facilitating communication between a plurality of sensors and a central monitoring unit in sports and health monitoring devices, to allow for better analysis of the performance of an athlete or a patient.
The underlying idea of the invention is to take advantage of superimposed measurement signaling on a continuous DC power signal. The signal may be in analogous or in digital form or both. The invention is in other words based on messaging sensor-derived data from a plurality of sensors to communication modules, which are capable of receiving information from the sensors with a minimum of wiring, and on the identification of the sensors. It is known to superimpose or multiplex digital signals onto the same wire or set of wires as DC or analog signals. In heavy process industry, a system based on the Bell 202 standard is known as the HART protocol, which is also a standard (IEC 61158). It is a master/slave protocol, meanings that a slave device only speaks when spoken to by a master. The protocol implements the Open System Interconnection (OSI) 7-layer protocol model using frequency shift keying (FSK) to communicate at 1200 bps with a signal having bit values of 0 and 1 at 2200 and 1200 Hz, respectively. This signal is superimposed at a low level on the 4-to-20 mA analog measurement signal. Such signals may contain data such as device data, requests for device data, configuration data, alarm and event data, etc.
Another example is presented in the Digital Command Control (DCC) protocol of German origin that has been adapted, developed and standardized by the National Model Railroad Association (NMRA). It provides for individually command of several trains running on a track having a single power feed by modulating the DC voltage on the track to encode digital messages while providing electric power, thus providing independent identification and control of locomotives without special wiring requirements. The DCC technology has been further developed e.g. in U.S. Pat. No. 6,494,410, where a train after having received a DCC control information specifically addressed to it, applies a return signal with a higher frequency to the track, and which is detected by synchronizing its detection with the original DCC square wave voltage so that the return signal is detected in periods where the DCC signal is free of signal edges.